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If you fly even just a couple times a year, it's worth having an airline credit card.

These cards come with perks and benefits that come with these cards, such as free checked bags, priority boarding, or lounge passes, that make flying easier and more enjoyable — and can save you money.

We compared some of the most popular mainstream credit cards from the three big US airlines — American, United, and Delta.

While a card that earns transferable points — like the Chase Sapphire Preferred— typically has more valuable and flexible rewards than fixed program cards, airline cards win in two respects.

If you generally fly with one preferred airline and earn frequent flyer miles on that program when you travel, it can make sense to earn the same kind of miles from your credit card. Between the mileage earned from both, your miles will add up quicker.

Also, airline credit cards come with various perks specific to that airline that can save you a ton of time and money. Things like complimentary checked bags, priority boarding, and even day passes to airport lounges will have you feeling like you're flying first class even when you're in basic economy.

Each of the three major US airlines (American, Delta, and United) offer a few different credit cards, but among the most popular are the "mainstream" cards. These products have annual fees between $95 and $99 — often waived the first year — and feature benefits that appeal to everyone from casual fliers to road warriors.

While they all have similar features and benefits and all offer a great value to cardholders, we've compared them and found that one stands out above the rest. Read on to see which one it is.

Keep in mind that we're focusing on earning rewards and perks, not things like interest rates and late fees, which can far outweigh the value of any rewards or benefits.

When you're working to earn credit card rewards or take advantage of travel benefits, it's important to practice financial discipline, like paying your balances off in full each month, making payments on time, and not spending more than you can afford to pay back — or spending more than you would otherwise. Basically,treat your credit card like a debit card.

First up is American Airlines: the Citi/AAdvantage Platinum Select World Elite Mastercard.

Currently, Citi and American offer a sign-up bonus of 50,000 American Airlines AAdvantage miles when you spend $2,500 in your first three months with the card.

50,000 miles (or at least 52,500, when you factor in the miles you'll earn for completing the minimum spending requirement) can get you far on American Airlines — as long as you can find "SAAver" availability. Based on American Airlines' award chart, it's nearly enough miles for a round-trip flight to Europe or South America during peak season, a one-way ticket to Europe in business class, or at least two domestic round-trips (or more, depending on the distance).

The Citi/AAdvantage Platinum card earns 2x miles per dollar spent on American Airlines purchases. Citi also recently added a few new bonus categories — new card members will earn 2x miles on restaurants and at gas stations, too (existing card members started earning at the new rate in July). You'll earn 1x mile on everything else.

The card comes with a suite of useful benefits for American Airlines flyers.

You and up to four companions traveling on the same reservation each get a free checked bag on domestic flights (since American Airlines is a full-service carrier, most international flights include the first checked bag for free). Because the first checked bag is usually $25 each way, this benefit can save you $50 on a round-trip itinerary.

In addition, you and everyone on your reservation get preferred boarding — joining an earlier boarding zone. That gives you more time to settle in — and earlier access to the overhead bins, so that you can make sure you'll have room to store your bag.

A small, but useful new perk: When you spend $20,000 or more on the card in a card membership year, you'll get a $100 discount on your next American Airlines flight (that's in addition to the miles you'll earn on those purchases).

The card also offers a 25% discount on in-flight purchases, such as food and drinks, and access to discounted mileage award flights. Until recently, cardholders also got 10% of all redeemed miles back each year up to 10,000 miles. However, American recently announced that it was pulling this perk.

Next is the United Mileage Plus Explorer Card.

The United Explorer card offers 40,000 United miles when you spend $2,000 in the first three months. While the card has occasionally offered higher targeted bonuses, those don't always waive the $95 annual fee for the first year — this current public offer does.

Like the other airlines' sub-$100 cards, the United card offers a free checked bag for the cardholder. Up to two traveling companions booking at the same time can also get a free checked bag each. This is especially useful since United recently raised the price of a checked bag to $30.

Unlike the other airlines' cards, though, you'll have to actually buy the tickets with the United card in order to get the free checked bags — simply having the card open and tied to your account isn't enough.

For those who don't have luggage to check, the card offers priority boarding for everyone on your reservation — you'll get this benefit even if you pay for the tickets with another card. By boarding earlier, you can make sure to snag overhead space for your carry-on.

One excellent perk with the United card is that you'll get two complimentary passes to United Club lounges each year. If you get to the airport early or end up dealing with a delay, you can head to the lounge and enjoy free snacks, drinks, Wi-Fi, and more comfortable seating than what you'd find in the terminal.

When you spend $25,000 in a calendar year, you'll also get a PQD waiver — PQDs, or "Premier Qualifying Dollars," count toward earning elite status with the airline. When that requirement is waived, you'll earn status just based on how much you've flown, rather than a combination of how much you've flown and how much you've spent that year.

The card earns 2x miles per dollar spent on all United purchases, and following the card's rebranding in June, it also earns 2x miles on all dining and hotel spending. It will continue earning 1x mile on everything else. There are no foreign transaction fees.

Other features include a fee credit to cover the cost of enrolling in Global Entry/TSA PreCheck, and a 25% discount on all in-flight United purchases.

One unique — but unpublished — perk of the card is that having it helps you access additional United award space. That means that you'll have an easier time finding the flights you want when it's time to actually use your miles.

Finally, there's the Gold Delta SkyMiles Card from American Express.

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Until April 3, the Gold Delta Amex is offering 60,000 bonus Delta SkyMiles when you spend $2,000 on purchases within the first three months. You'll also get a $50 statement credit if you make any Delta purchase with the card within the first three months. In terms of points, this is the highest-ever public offer on the Gold card.

In addition to the welcome offer, the card comes with a handful of incredibly useful — and valuable — perks.

If you have the card open, you get a free checked bag on Delta flights, as does each other person on your reservation. Delta normally charges $30 for the first checked bag on each flight — so $60 for a round-trip — meaning that for a family of four, the free checked bag benefit could save $240.

The card also offers priority boarding to everyone on the cardholder's reservation. If you aren't checking a bag, that can come in useful — by boarding a little earlier, you'll get better access to the overhead compartments and won't have to worry about space running out.

American Airlines: the Citi/AAdvantage Platinum Select

Free first checked bag for you and up to four traveling companions, regardless of whether or not you use the card to buy your tickets

Priority boarding

$100 discount on an American Airlines flight if you spend $20,000 in a year

Discount on in-flight purchases

Cons:

No lounge passes or discounts

No spending bonus that counts towards elite status

United Airlines: the Explorer Card from Chase

Pros:

2x miles on dining and hotels, as well as on United purchases

Two complimentary United Club lounge passes each year

Priority boarding for you and your travel companions

Discount on in-flight purchases, Global Entry/TSA PreCheck credit

Access to additional saver-level award seats

Cons:

To get the first checked bag free, you'll have to use the card to buy your tickets

The free checked bag is only extended to up to two traveling companions — that's not helpful if you're traveling with a family of four

Delta: the Gold Delta SkyMiles card from American Express

Pros:

Free first checked bag for you and any traveling companions, regardless of whether or not you use the card to buy your tickets

Priority boarding

Discounted day passes for Delta Sky Club lounges

Discounts on in-flight purchases

All-time highest public welcome offer (until September 19)

Cons:

No bonus earning categories (besides Delta purchases)

No extras (like a discount on flights, extra points, or help toward elite status) if you spend a lot on the card in a year

5/

So, which is best?

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The best card is the one for whichever airline you find the most useful. Although there are some differences between them, each of these cards comes with a version of free checked bags and priority boarding, which are the most valuable reasons to have the cards. Plus, they help you earn more miles — and quickly.

However, if you're ambivalent about your choice of airline, the Citi/AAdvantage card for American Airlines is probably the most appealing card right now.

Between the new benefits, including 2x points at several new categories, and a solid sign-up bonus, this card represents a great value. However, keep in mind that it's always possible that the sign-up bonus increases at some point in the future, although there's no guarantee.

In a similar vein, the current limited-time welcome offer on the Gold Delta card makes now an ideal time to open it.

As benefits continue to be added and removed — and, crucially, as sign-up bonuses and welcome offers fluctuate — this evaluation could always change. One way or another, an airline card is a must-have and represents significant value for anyone who flies even just a few times a year.

This content is not provided by the card issuers. Any opinions, analyses, reviews or recommendations expressed here are those of the authors' alone, and have not been reviewed, approved or otherwise endorsed by any issuer.

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